1. Field of the Invention
This invention relates to a rotary telephone dial.
2. Description of the Prior Art
In conventional rotary dials, shafts including a main shaft to a governor shaft of a rotary system for driving an impulse generating function and a governor function, which are principal functions, are individually provided so that parts are complicatedly assembled and engaged with one another. Accordingly, the number of parts is very large and, of course, the number of assembling steps is also very large. Namely, the construction of the conventional rotary dial requires many assembling steps, such as insertion of rotary shafts of a gear system into predetermined holes, insertion of a shaft carrying element or mounting thereon a sub-assembly of parts into a predetermined hole, providing studs for limiting play and falling of the shafts in the direction of their thrust, etc. Moreover, many screws, rivets, etc. are used in addition to caulking at many places to fix parts, so that the conventional rotary dials cannot easily be assembled and require large-scale production equipment.
Further, the allowable angular range of a finger moving operation for generating normal dial pulses is about 4.degree. (1/2 of 1/3 of fourteen equal divided parts from the outer periphery) at maximum. For example, in a case where the finger moving angle of the dial is insufficient, an impulse cam directly coupled with a finger plate is not sufficiently rotated, so that the length of the first break pulse is reduced. Conversely, in case of an excessive finger moving angle, the impulse cam is excessively rotated to produce a pseudo-pulse in some cases. This generates incorrect pulses to cause an erroneous switching, which is a fatal defect of the dial function. Further, since the allowable angular range of the finger moving operation is narrow, high accuracy is required of the parts and assembling.
Moreover, a spring retaining structure in the conventional rotary dial is of the type in which required contact springs and insulating plates are alternately placed one on another and fixed to a frame. Each clamping screw for fixing them is usually inserted through an insulating tube to provide insulation between the contact springs. This kind of contact spring retaining structure involves a large number of assembling steps. Moreover, an increase in the number of contact circuit springs increases the number of insulating plates for insulating the contact springs from each other and requires to change the length of the insulating tube coupling screw. With such a structure, if the telephone set is installed at a dry place, coupling becomes loose due to shrinkage of the insulating plate to introduce the possibility of an erroneous operation of the contact spring. Conversely, at a place of high humidity, the insulating plate expands to break down the coupling screw.
Further, in a governor mechanism of the conventional rotary dial, a flying bar is mounted in a cylindrical governor cup closed at one end and two opposing governor weights are disposed on the upper surface of the flying bar. In this case, these governor weights are rotatably supported by inserting support pins into holes of support portions at both ends of each governor weight and fitting the top ends of the pins into holes of the flying bar. A governor spring is retained at one end to a retaining pin disposed on one of the governor weights and at the other end to a retaining pin on the other governor weight, thereby to provide the function which prevents by resiliency of the governor spring a phenomenon that, during dial free moving, the governor weights are rotated to be spread too far from their support pins due to the centrifugal forces, in other words, the governor weights are positioned in a normally spaced relationship relative to each other. With such a construction, however, assembling includes caulking of the support pins to the flying bar, and oiling between the apertures and the support pins, and hence is troublesome. If the support pins are caulked too much, there is the possibility of such a trouble that the governor weights do not rotate smoothly.
Moreover, in such a construction, when resiliency of a governor spring is required to be changed for adjustment of the rotational speed, the governor spring must be replaced by another one. Moreover, in such a construction, it is necessary to assemble a friction piece and a retaining pin with the governor weight by pressing or caulking. Further, positioning accuracy is required of a support ring, the friction piece and the retaining pin of the governor weight, and the friction piece and the retaining pin are opposite in the direction of assembling, so that simplification of the manufacture process has been desired.